1. Field of the Invention
The invention relates to an impregnator for mixing a nonaerated or only slightly aerated liquid with a gas. The invention also relates to a pressure compensator assembly for bar systems, an impregnator for inline gassing bar systems, and a bar system with a pressure compensator assembly. The invention further relates to novel uses of such an impregnator. The nonaerated or only slightly aerated liquid may be a soda, soft drink, water, juice, or a low-carbon-dioxide or carbon-dioxide-free beer precursor product. The gas be carbon dioxide or nitrogen.
2. Description of Related Art
Impregnation in terms of the invention is the release of gases into liquids, or in other words impregnating liquids with gases, as it is carried out in absorption columns in large-scale chemical systems. For example, according to the German Patent DE 25 03 681, a gas is conducted from the bottom of a column to the top of the column in counter current to a liquid, which flows from the top to the bottom, wherein the column is filled with a porous ceramic material.
Such impregnators are used in bar systems, so that liquids or beverage precursor products can be impregnated with gases, or gases can be released into the liquids and beverages ready to drink can thus be produced, but only once they are in the bar system. Examples of liquids to be impregnated, sodas (syrups) and in particular a low-carbonation or carbonation-free beer precursor product can be considered. Besides gases that contain flavorings, in particular carbonic acid (more precisely, CO2) and nitrogen (more precisely, N2) can be considered as impregnating gases, in particular for creating a bubbly soda and in particular a carbonated beer.
The term “carbonic acid” or “carbonated” is indeed usual in beverages, but more precisely, carbon dioxide (CO2) is added, which by far predominantly bonds only physically in the liquid and does not enter into any chemical reaction to form carbonic acid (H2CO3).
This physical bond upon the release of gases into liquids is a mass transfer process in accordance with the laws of physical absorption. This transfer process takes place at the gas-liquid phase boundary faces. The gas diffuses into the liquid. While nonpolar nonelectrolytes, such as oxygen and nitrogen, on becoming dissolved are incorporated primarily into the voids between the liquid molecules, polar electrolytes, such as carbon dioxide, in water form water bridges with the likewise polar water molecules, and these bridges cluster with other water molecules to form supermolecular assemblies. CO2 molecules, for example, penetrate the microstructure of the water molecules quite well. The mass transfer of gases into liquids is described in simplified form in Fick's first law:Mi=A(Ci*−C1)=(Di/δi)Aξ(Pi*−P1).In the equation,
Mi stands for the mass flow of a gas from the gas phase into the liquid;
A stands for the area of the surface at which the mass transfer takes place;
(Ci*−C1) stands for the concentration gradient between the equilibrium concentration at the phase boundary face and the instantaneous concentration in the liquid;
δ stands for the length of the transportation course from the interior of the liquid to the phase boundary face;
Di stands for the diffusion coefficient for gases;
ξ stands for the absorption coefficient (of the solubility of gases) as a function of temperature, pressure, and material; and
(Pi*−P1) stands for the pressure drop between the partial pressure of the gas and the pressure applied at that instant in the liquid.
Accordingly, the speed (Mi) at which a state of equilibrium is established in a liquid depends on the concentration gradient, the diffusion coefficient for gas, the absorption coefficient, the surface area, the length of the transportation course, the prevailing pressure, and the temperature.
Efficient mass transfer systems must therefore have a large surface area where the mass transfer can take place, must create high turbulence for the shortest possible transportation courses, and must furnish both high pressure and low temperatures, so as to attain the most efficient and fastest possible mass transfer in one phase.
Besides known bubble-forming systems, such as agitation systems, loop reactors or injection systems, which are not very economical because of their vulnerability and in particular the high expense for equipment in injection systems (pressure vessel, pressure pump, cooling system) and the attendant high operating costs, carbonators or impregnators of the type defined at the outset have become established in the field of gassing beverages with carbonic acid in bars and pubs.
By means of a predetermined gas and liquid pressure—in the impregnation of an uncarbonated beer precursor product with CO2, a liquid pressure of 4 bar and a gas pressure of 5 bar, for instance, or a liquid pressure of 5 bar and a gas pressure of 5.5 bar, have proven suitable—the attempt is made to establish the desired ratio of gas to liquid in the mixing cell and an optimal pressure in the mixing cell, so that the desired dissolution of the gas in the liquid takes place.
However, such impregnators are often used in inline gassing bar systems, in which the beverage precursor product is conventionally pumped out of a tank with piston pumps and more recently also from a bag using diaphragm pumps, so that the impregnator is exposed on the inlet side to the pressure surges of the piston pump, and a constant fuel pressure cannot be attained. The volumetric flow discharging into the mixing cell per unit of time therefore depends substantially on the speed with which the bartender taps the beverage. If the tapping speed changes, the pressure drop from the gas infeed or liquid infeed side to the mixing cell changes as well, so that the degree to which the gas infeed and liquid infeed open fluctuates even though the external pressure is set to a fixed value. As a result, the volumetric flows discharging into the mixing cell change as well, so that the gas-liquid mixture ratio may deviate from the optimum for dissolution of the gas in the liquid at whatever pressure prevails in the mixing cell.
In bar systems, a beverage is pumped via a beverage infeed line from a beverage container to a dispensing tap, usually located at a higher level. In conventional bar systems, the beverage infeed line comprises a bar line; in bar systems with inline gassing, or pressure gassing stages in the bar, one or more impregnators may also be disposed in the beverage infeed line, and with them a beverage precursor product is enriched for instance with carbonic acid. In so-called postmixing bar systems, mixing valves for syrup with an inline-aerated water can be located in the beverage infeed line, along with a buffer container in which the water is aerated in a carbon dioxide atmosphere.
An impregnator, wherein water is impregnated with a carbon dioxide under a carbon dioxide atmosphere is disclosed in U.S. Pat. No. 636,162. The gas and the liquid pass through wire-cloth sieves and the impregnated liquid gas mixture is conducted in a buffer container.
For pumping the beverage or beverage precursor product through the beverage infeed line, a defined pumping pressure is necessary. In conventional bar systems, this pressure is furnished for instance via a compressed gas (such as carbon dioxide), whose pressure is exerted on a beverage keg or drink container, so that the beverage is forced upward to the dispensing tap via the dispensing line. In bar systems with a pressure gassing stage in the bar, which operate by the inline carbonation process and in which a so-called impregnator is provided in order to provide a low-carbonic acid or carbonic acid-free beverage precursor product in the bar system with carbonic acid or the like, conversely the beverage container is followed downstream by a pump, with which the beverage precursor product is pumped out of the beverage container to the impregnator and becomes carbonated there, or in other words mixed with carbonic acid (or more precisely, carbon dioxide), so that then it can be pumped as a beverage, with the carbonic acid dissolved in it, to the dispensing tap.
This requires a certain working pressure, which is above the keg pressure and the dispensing pressure. In inline gassing of beer, for instance, a pressure in the impregnator of 4 to 5 bar has proved suitable.
To enable adjusting the desired tapping speed of the dispensing tap, it is therefore necessary to artificially increase the pressure loss in the bar system, so that for instance an overly high pumping pressure, or the overpressure necessary for the inline gassing, is reduced, for instance to the keg pressure level that is usual in conventional bar systems. In conventional beer dispenser systems, for instance, a maximum of 1.5 to 3 bar, often 2.2 to 3 bar, of keg pressure is typical.
One possibility for this is to wind up the line in the form of a coil. So-called pressure compensators are also known, which today are usually directly integrated with the dispensing tap. In that case, a displaceable throttle restriction is disposed in the line leading to the dispensing tap, and its location can be adjusted by the bartender via an adjusting screw in such a way that the throttle restriction opens up an annular gap of a desired thickness, and the resistance can thus be varied and adapted to the desired conditions. With the adjusting screw, the bartender sets the dispensing tap to a desired flow rate, which is oriented for instance to whether he wants to fill large vessels, such as 1-liter steins, or small vessels, such as 0.25-liter soda glasses, and also depends on the liquid to be tapped, such as pale beer versus wheat beer.
Especially in bar systems with a pressure gassing stage in the bar, in which systems a working pressure in the impregnator is required that is above the keg pressure that is usual in conventional bar systems, the problem arises that regulating the quantity is no longer readily possible at the dispensing tap. If the bar system is used for beer, the beer “rips open”, or in other words begins to foam since carbonic acid is being released. This release is due to the fact that the dispensing tap pressure compensator is designed for a certain pressure range. If the line pressure is markedly higher than intended, the laminar flow is impeded, and eddies occur as a consequence of which carbonic acid is released.
If a compressed-air diaphragm pump is used at the dispensing tap, fluctuations in the pumping pressure can also occur. The tap pressure, however, should be constant, since otherwise, if pressure fluctuations occur, an unwanted release of carbonic acid can occur.
The U.S. Pat. No. 6,712,342 B2 and U.S. Pat. No. 6,138,995 disclose beverage dispensers, wherein hollow fiber membranes or bundles are provided. The hollow fiber membranes or bundles contain hydrophobic hollow fibers, which serve as impregnator bodies. CO2 passes through the impregnator bodies and the liquid to be impregnated washes round the impregnator bodies. Only the gas can pass through the walls of the hollow fibers and impregnates thereby the liquid on the other side of the wall.
An impregnator of this kind is proposed for instance in German Patent Disclosure DE 198 51 360 A1. This involves a tubular sieve carbonator, in which many mixing sieves are lined up with one another in a mixing cell, embodied as a tube, to which the gas and liquid infeeds can be connected. The mixing sieves together offer the desired large surface area at which the mass transfer can take place upon dissolution of the carbonic acid in the beverage precursor product. A tubular sieve carbonator of this kind can also be found in German Patent Application DE 100 55 1371 A1.
In U.S. Pat. No. 3,761,066 as well, a tubular sieve carbonator of this kind is shown, in which the gas and water supplied has to flow through a plurality of wire cloth mixing sieves: Gas is fed in from the side and water from above. The gas passes through a filter and an adjoining nozzle or impact plate to reach a prevortexing stage that the liquid also enters, namely through openings in the circumference of a cylindrical perforated plate. The flow thus created passes through openings in a conical perforated plate to enter the actual impregnation stage. Cylindrical wire cloth rings are located there, and plates are disposed between the individual wire cloth rings, so that the flow experiences a slalom through the wire cloths and in the process is impregnated. The annular wire cloth elements may be formed of any material that has (liquid-) permeable properties and is suitable for use in the carbonator shown.
Such tubular sieve carbonators, however, are not only relatively expensive in terms of material costs because of the high number of metal sieves but are also expensive with regard to the correspondingly complex assembly.
Recently, bulk material carbonators have therefore also been proposed, for instance in German Patent Application DE 101 60 397 A1. From this reference, a bulk material carbonator is found, with a mixing cell that is filled with a bulk material that has a high surface area, such as quartz pellets or the like. Other granular materials have also been proposed as the bulk material, such as fine plastic pellets or fine steel pellets made by VA Stahl. The surface area attainable with the bulk material, however, is still limited. This is because floating of the bulk material out of the impregnator must absolutely be avoided, at least in the field of foodstuffs, and thus the bulk material, despite the requirement for a large surface area, cannot be allowed to be ground arbitrarily fine so as not to clog the requisite trapping systems for the bulk material. Nevertheless, clogging cannot be completely avoided over the course of time, and bulk material carbonators must therefore be replaced relatively often. It is also disadvantageous that such bulk material carbonators are relatively difficult to clean, so that at the cleaning intervals necessary for reasons of food hygiene, especially in connection with beverages containing starch or sugar, usually the entire bulk material carbonator has to be replaced.